A design method for evaluating the corrosion resistance of metals in frozen soil environments

Abstract

The present invention relates to a design method for evaluating the corrosion resistance of metals in a frozen soil environment, which belongs to the technical field of metal corrosion simulation evaluation. It solves the problem in the prior art that there is no reliable evaluation and preliminary screening technology for the corrosion resistance of metals in a frozen soil environment, and lacks guidance / design methods for establishing the above-mentioned technology. The present invention provides a design method for evaluating the corrosion resistance of metals in a frozen soil environment, including the steps of information collection, equipment design, simulated corrosion solution and temperature curve design, full immersion corrosion experiment, corrosion rate calculation, etc. The design method provides an idea for evaluating the corrosion resistance of metals in a frozen soil environment, and specifies the specific implementation steps and parameter design methods. The simulation method established according to the design method can preliminarily evaluate and compare the corrosion resistance of different types of metal materials in a frozen soil environment, and provide support for the selection and development of metal materials for equipment or construction in a frozen soil environment.

Description

Technical Field

[0001] The present invention relates to the technical field of metal corrosion simulation evaluation, and in particular to a design method for evaluating the corrosion resistance of metals in a frozen soil environment. Background Art

[0002] With my country's economic growth, the development of western China has become a key focus for the next phase. Economic development is inseparable from infrastructure, so highway construction in the high-altitude and cold regions of western my country has also been prioritized. Compared to eastern China, western China's high altitude, low temperatures, and extensive permafrost create extremely harsh conditions for road foundation construction, making the construction and maintenance of high-grade highways extremely difficult.

[0003] To address the challenges of highway construction and lifespan in permafrost regions, improvements in construction methods and structural optimization are being made to increase road foundation stability, reduce and prevent uneven road settlement, extend service life, minimize maintenance, and lower the overall cost of the road's entire lifecycle. This inevitably increases the use of steel in road structures, primarily in the following categories: guardrails, road signs, and other auxiliary facilities for road safety; rebar, steel pipes, and steel plates for road foundation construction; and steel plates, profiles, and cables for bridge construction.

[0004] In addition to steel for permafrost roads, the number of equipment installed in permafrost environments for scientific research or other special needs is also gradually increasing; for example, high-end equipment used for environmental monitoring, seismic wave monitoring, geological exploration or other special purposes, especially high-end equipment that needs to be buried or semi-buried underground, also requires specific material selection based on environmental conditions.

[0005] Corrosion is a major factor in steel failure, and steel's corrosion resistance determines material usage and maintenance and replacement cycles. Generally speaking, materials with poor corrosion resistance are designed with sufficient margins, increasing material usage and construction costs. For replaceable components, poorly resistant materials shorten their service life and increase replacement frequency, thus increasing maintenance costs. Therefore, selecting appropriate materials based on regional conditions, accurately evaluating their corrosion resistance, and predicting their service life, combined with a comprehensive consideration of material manufacturing, construction, and maintenance costs, are effective methods for reducing the overall lifecycle costs of metal materials in permafrost environments.

[0006] At present, there is still a gap in how to simulate and evaluate the corrosion behavior of metal materials in permafrost environments at home and abroad. Therefore, it is particularly necessary to develop a design method for evaluating the corrosion resistance of metals in permafrost environments. Summary of the Invention

[0007] In view of the above analysis, an embodiment of the present invention aims to provide a design method for evaluating the corrosion resistance of metals in permafrost environments, so as to solve the problems in the prior art of the lack of reliable evaluation and preliminary screening technology for the corrosion resistance of metals in permafrost environments and the lack of guidance / design methods for establishing the above technology.

[0008] The present invention provides a design method for evaluating the corrosion resistance of metals in a frozen soil environment, which specifically comprises the following steps:

[0009] S1: Collect monthly temperature curves, air pressure variation range, atmospheric composition, hydrology and soil composition information of the area to be simulated;

[0010] S2: Design and prepare a test device based on the upper and lower limits of the temperature curve, determine the composition of the simulated corrosion solution based on the hydrological and soil composition information, and prepare the simulated corrosion solution;

[0011] S3: Preset the temperature curve according to the annual and monthly temperature curves, and adjust the gas atmosphere inside the testing device according to the air pressure variation range and the atmospheric composition information;

[0012] S4: The metal to be tested is made into a metal sample of a certain specification, and a full immersion corrosion simulation experiment of at least one temperature curve cycle is carried out using the test device and the simulated corrosion solution. The corrosion behavior and corrosion resistance of the corresponding metal in a frozen soil environment are estimated based on the corrosion simulation results; wherein, one temperature curve cycle is 24 hours.

[0013] Specifically, the maximum temperature of the monthly temperature curve is not higher than the local freezing point, and the difference between the upper and lower limits of the monthly temperature curve is T max -T min ≤10℃, it is determined that the simulated area is a constant temperature frozen soil environment in the corresponding time period.

[0014] Specifically, the difference between the upper and lower limits of the monthly temperature curve is T max -T min >10℃ and the maximum temperature T max ≤ local freezing point T0, it is determined that the simulated area is in an alternating freezing environment during the corresponding time period;

[0015] The difference between the upper and lower limits of the monthly temperature curve T max -T min >10℃ and the maximum temperature T max >Local freezing point T0, and T max -T0<T0-T min When , it is determined that the area to be simulated is an alternating and gradual melting environment in the corresponding time period;

[0016] The alternating freezing environment and the alternating gradual thawing environment are collectively referred to as alternating low-temperature permafrost environment.

[0017] Specifically, the maximum temperature T of the monthly temperature curve max >Local freezing point T0 and minimum temperature T min < local freezing point T0, and T max -T0≥T0-T min When the temperature drops to 0.05, it is determined that the simulated area is in a short-term frozen ground environment during the corresponding time period.

[0018] Specifically, different months in the area to be simulated may belong to different permafrost environment types, and the actual simulation evaluation can be implemented by combining different types of temperature curve cycles.

[0019] Specifically, a temperature curve of alternating low-temperature frozen soil environment used to simulate the environment of the northeastern Mohe basin in December is:

[0020] The temperature curve range is between -35°C and -20°C, and the preset initial temperature is -20°C;

[0021] Phase 1: Target temperature -35±1℃, cooling rate 0.5~10℃ / hour, keep warm after reaching the target temperature, for a total of 12~16h;

[0022] Phase II: Target temperature -20±1°C, heating rate 0.5-5°C / hour, keep warm after reaching the target temperature, for a total of 8-12 hours;

[0023] With a 24-hour cycle, the total detection time is 1 to 30 days.

[0024] Specifically, the internal gas atmosphere includes nitrogen and oxygen, Vnitrogen:Voxygen=7-8:3-2, and the internal gas atmosphere pressure is 50-100 kPa.

[0025] Specifically, the specific operations of step S4 are:

[0026] S4-1: Make the metal to be tested into metal samples of certain specifications, weigh the metal samples and record the weight;

[0027] S4-2: Completely immerse the metal sample in the simulated corrosion solution, place the container containing the simulated corrosion solution in a closed simulation chamber and pre-temperature it;

[0028] S4-3: According to a preset temperature curve, a temperature-controllable circulating gas is introduced into the closed simulation chamber to adjust the temperature in the simulation chamber and start timing, so that the temperature in the chamber changes according to the preset temperature curve;

[0029] S4-4: After the preset detection time is reached, the corroded metal sample is taken out and cleaned to remove the surface corrosion part, and the corrosion amount is calculated based on the weight difference before and after.

[0030] Specifically, the simulated corrosion solution comprises, by mass percentage, 0.06-1% Na2SO4, 0.05-0.1% MgCl2, 3-5% NaCl, and the remainder is deionized water; the pH value of the simulated corrosion solution is 6-8.

[0031] The present invention also provides a device for implementing the simulation evaluation method designed by the design method: the device comprises two parts: a temperature control module (1) and a simulation test module, the temperature control module is used to control the temperature change inside the simulation test module, and the simulation test module is used to implement a full immersion corrosion simulation corrosion test of a metal sample.

[0032] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0033] 1. The design method disclosed in this invention provides for the first time an idea for evaluating the corrosion resistance of metals in a frozen soil environment, and specifies the specific implementation steps and parameter design methods.

[0034] First, design and prepare simulation equipment that meets the implementation requirements based on the temperature variation range of the area to be simulated. Then, design a temperature variation curve based on the actual local all-day variation curve to make the simulated temperature conditions as close to reality as possible. It is worth noting that, generally speaking, the variation of the local temperature curve is related to the sunshine time, so the time of a single temperature cycle is set to 24 hours, and the heating and cooling time and speed are adjusted according to the actual curve. According to the local hydrology and soil composition of the area to be simulated, identify the ions that play a major role in metal corrosion and prepare a simulated corrosion solution.

[0035] In addition, since metal materials are actually buried or semi-buried underground, the influence of atmospheric corrosion is relatively small, and its influence is omitted in the present invention; however, oxygen in the atmosphere has an important influence on metal corrosion in the soil. It not only participates in the metal oxidation reaction, but also acts as an electron acceptor in the corrosion process, accelerating the occurrence and development of corrosion. The corrosion rate of oxygen on metals increases with increasing temperature and concentration, and the presence of water will also accelerate the corrosion rate of metals. In order to restore the air pressure conditions of the permafrost environment as much as possible (generally speaking, permafrost environments are mostly plateaus with low air pressure) and atmospheric components, the present invention can adjust the composition and air pressure of the circulating gas so that the simulated corrosion process is as close to the actual situation as possible;

[0036] It is worth emphasizing that existing full immersion corrosion simulation experiments generally ignore the regulation of gas atmosphere. However, since permafrost areas are often located at high altitudes or high latitudes, the air pressure and air composition ratio are significantly different from those in plains or low-altitude areas. Therefore, the influence of air / atmosphere must be taken into account when simulating the corrosion resistance of metal materials in permafrost environments.

[0037] The present invention comprehensively considers specific environmental factors and restores the real environmental corrosion mechanism as much as possible, appropriately simplifies some minor influencing factors, and strives to simulate and evaluate the metal corrosion behavior in frozen soil environment through simplified simulation conditions and operation processes.

[0038] 2. According to the environmental characteristics of the specific area being simulated, the temperature curve can be further optimized during the design process to achieve targeted simulation of constant temperature frozen soil environment, alternating low temperature frozen soil environment, and short-term frozen soil environment; according to the hydrological information of the specific area, the composition of the simulated corrosion solution can be adjusted, the concentration of each component can be adjusted, and appropriate amounts of other components or even sand and gravel can be added, thereby achieving targeted restoration and simulation of metal corrosion behavior in specific areas, and the evaluation results are more accurate and targeted.

[0039] 3. The present invention provides a supporting device for the above-mentioned evaluation method, wherein the device comprises a temperature control module and a simulation test module, the two parts being independent of each other and having no physical connection;

[0040] The temperature control module uses a reverse Carnot cycle to control the temperature of the simulation test module by redirecting heat flow. The first heat exchanger, placed in an environment, can exchange heat with the atmosphere. This first heat exchanger uses an isolated design to exchange heat with the simulation test module (primarily the second heat exchanger), thereby achieving temperature control of the simulation test module while avoiding the presence of corrosive gases in the temperature control module.

[0041] When cooling is needed, the heat pump transfers heat from the second heat exchanger to the first heat exchanger. After the second heat exchanger cools down, it absorbs heat from the closed simulation chamber circulation system, causing its own temperature to drop. After the first heat exchanger absorbs heat, its temperature rises and it releases it to the surrounding atmosphere. When heating is needed, the heat pump reverses, and heat flows from the first heat exchanger to the second heat exchanger. At this point, the first heat exchanger cools down and absorbs heat from the surrounding atmosphere. After the second heat exchanger acquires heat, its temperature rises and it releases heat to the simulation chamber circulation system, raising its own temperature. The second heat exchanger itself is equipped with an electric heater. If the surrounding heat is insufficient, the heater can provide auxiliary heating to quickly raise the temperature of the simulation chamber.

[0042] Since the corrosive reagent is volatile to a certain extent, the circulating gas contains certain corrosive components. The closed simulation chamber in the simulation test module adopts a closed design and is made of corrosion-resistant materials, and a protective layer is attached to the outer surface. To protect the internal equipment and the surrounding environment, the temperature control module and the simulation test module adopt an isolated design. The two exchange heat through a heat exchange system to prevent the simulated gas from affecting the temperature control module.

[0043] The above-mentioned device can perfectly adapt to and meet the implementation requirements of the evaluation method provided by the present invention, thereby realizing a preliminary simulation of the corrosion behavior of metals in a permafrost environment in a laboratory scenario, and can make a preliminary comparison and screening of the corrosion resistance of different metal materials in a permafrost environment, and can also provide support for the subsequent development of metal materials.

[0044] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0046] Figure 1 Schematic diagram of an apparatus (cooling mode) for implementing the simulation evaluation method;

[0047] Figure 2 This is a schematic diagram of the temperature control module (heating mode);

[0048] Figure 3 Schematic diagram of the reagent tank;

[0049] Figure 4 This is the average temperature curve of Mohe in December.

[0050] Reference numerals:

[0051] 1. Temperature control module; 11. Four-way reversing valve; 12. Compressor; 13. Radiator; 141. First expansion valve; 142. First one-way valve; 151. Second expansion valve; 152. Second one-way valve; 16. First heat exchanger; 2. Closed simulation chamber; 21. Second heat exchanger; 22. Circulation fan; 23. Sample cell; 24. Negative pressure filter; 25. Sensor. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0053] In geology, permafrost refers to various rocks and soils below 0°C that contain ice. It can generally be categorized as short-term frozen ground (lasting a few hours, days, or even half a month), seasonal frozen ground (lasting half a month to several months), and permafrost (lasting more than several years). Permafrost is a temperature-sensitive soil medium that contains abundant ground ice and a certain amount of unfrozen water. This results in rheological properties, with long-term strength far lower than its instantaneous strength. Furthermore, with temperature fluctuations, permafrost constantly fluctuates between frost heave and thaw settlement, significantly impacting the safety of structures in permafrost areas.

[0054] Temperatures vary widely across permafrost regions. For example, the Qinghai-Tibet Plateau has an average monthly temperature of 6-18°C in its warmest month. Nearly a quarter of the northwestern region lies within the plateau frigid zone, with elevations above 5,000 meters. The annual average temperature ranges from -10°C to -4°C, with the warmest month averaged below 6°C. Nearly a quarter of the central and western regions lies within the plateau subarctic zone, with elevations mostly between 4,500 and 5,000 meters. The annual average temperature remains below 0°C, with the warmest month averaging 6-10°C. Meanwhile, Genhe City in Hulunbuir, Inner Mongolia, known as the "Cold Pole of China," has an average temperature of -5.3°C. In 2024, the highest temperature reached 34°C in July, and the lowest reached -45°C in January. The lowest temperature ever recorded was -58°C. This wide temperature range causes the surface permafrost to alternate between freezing and thawing, and the permafrost depth fluctuates seasonally, posing significant road safety risks.

[0055] The frozen soil state is affected by the ambient temperature and is unstable. It can be roughly divided into the following three types:

[0056] At low temperatures, the water in the permafrost freezes and turns into ice. Other components in the permafrost combine with the ice to form a relatively stable solid. The environment surrounding the steel is relatively stable at this time, but the pressure changes caused by expansion during the solidification process have a certain impact on the steel. The friction changes caused by expansion also have a negative impact on the metal's external protective layer. As temperatures rise, the strength of the frozen ice in the permafrost decreases with increasing temperature, and it melts when the temperature exceeds the freezing point of water. Because the thermal resistance of metal is much lower than that of soil, the permafrost surrounding the metal is the first to change during the warming process. The water and the substances contained in the water transform from a solid state to an ionic state. At this time, the corrosion effect on the metal increases with the increase in ion concentration. As the ambient temperature increases further, the permafrost completely melts and becomes fluid, and the corrosion caused by the environment is expected to be the strongest at this time.

[0057] Since the corrosion situation changes with the environment, the corrosion rate at different stages is difficult to obtain through simple calculations. Therefore, a set of devices and methods that can simulate the changes in the permafrost environment are needed to conduct simulation evaluation and quantitative evaluation of the corrosion amount.

[0058] The present invention provides a design method for evaluating the corrosion resistance of metals in a frozen soil environment, which specifically comprises the following steps:

[0059] S1: Collect monthly temperature curves, air pressure variation range, atmospheric composition, hydrology and soil composition information of the area to be simulated;

[0060] S2: Design and prepare a test device based on the upper and lower limits of the temperature curve, determine the composition of the simulated corrosion solution based on the hydrological and soil composition information, and prepare the simulated corrosion solution;

[0061] S3: Preset the temperature curve according to the annual and monthly temperature curves, and adjust the gas atmosphere inside the testing device according to the air pressure variation range and the atmospheric composition information;

[0062] S4: The metal to be tested is made into a metal sample of a certain specification, and a full immersion corrosion simulation experiment of at least one temperature curve cycle is carried out using the test device and the simulated corrosion solution. The corrosion behavior and corrosion resistance of the corresponding metal in a frozen soil environment are estimated based on the corrosion simulation results; wherein, one temperature curve cycle is 24 hours.

[0063] The simulation evaluation method can perform a preliminary simulation of the corrosion behavior of metals in permafrost environments in a laboratory setting. It can also conduct a preliminary comparison and screening of the corrosion resistance of different metal materials in permafrost environments, and can also provide support for subsequent metal material development.

[0064] There are many factors that affect the corrosion resistance of metals. It is generally believed that the corrosion system is composed of materials and the environment. The factors affecting corrosion can be basically divided into internal factors related to the material and external factors related to the medium environment. By simulating external environmental factors and using accelerated or simulated corrosion methods to study the corrosion of materials in specific environments, it is helpful to evaluate the corrosion resistance of materials and is helpful for the final application of the product. Under the premise of restoring the corrosion mechanism of the real environment as much as possible, the present invention appropriately simplifies some minor influencing factors, and strives to simulate and evaluate the corrosion behavior of metals in frozen soil environments through simplified simulation conditions and operating procedures. The simulated corrosion process is relatively close to the real corrosion process and has strong reference value.

[0065] Specifically, since the method of the present invention is mainly aimed at metal materials buried or semi-buried under frozen soil, a simulated corrosion solution and full immersion method are selected to perform corrosion simulation.

[0066] Specifically, by setting the temperature range and temperature curve, the temperature changes in the real environment are simulated. Since in the real environment, the temperature changes generally change in a "natural day" cycle and are closely related to the sunshine time, the temperature curve has a cycle of 24 hours.

[0067] Specifically, the temperature range is -70°C to 80°C, and changes according to a preset temperature curve. The temperature curve has a cycle of 24 hours, and the single detection time is 1 to 30 days, for example, 1, 2, 3, 5, 10, 15, 20, 25, and 30 days.

[0068] Specifically, the maximum temperature of the monthly temperature curve is not higher than the local freezing point, and the difference between the upper and lower limits of the monthly temperature curve is T max -T min ≤10℃, it is determined that the simulated area is a constant temperature frozen soil environment in the corresponding time period.

[0069] Optionally, when simulating a constant temperature permafrost environment, the temperature curve is set to a constant temperature, and the constant temperature is the same as the preset initial temperature; the temperature range is -70℃ to -10℃, for example, -70℃, -60℃, -50℃, -40℃, -30℃, -20℃, and -10℃. The temperature remains constant during the simulation process, and the temperature fluctuation is ≤1℃; the detection time is 1 to 30 days, for example, 1, 2, 3, 5, 10, 15, 20, 25, and 30 days.

[0070] Specifically, the difference between the upper and lower limits of the monthly temperature curve is T max -T min >10℃ and the maximum temperature T max ≤ local freezing point T0, it is determined that the simulated area is in an alternating freezing environment during the corresponding time period;

[0071] The difference between the upper and lower limits of the monthly temperature curve T max -T min >10℃ and the maximum temperature T max >Local freezing point T0, and T max -T0<T0-T min When , it is determined that the area to be simulated is an alternating and gradual melting environment in the corresponding time period;

[0072] The alternating freezing environment and the alternating gradual thawing environment are collectively referred to as alternating low-temperature permafrost environment.

[0073] Furthermore, when simulating an alternating low-temperature frozen soil environment, the temperature curve range is between -40°C and 5°C; the temperature change cycle is carried out in parallel with the temperature change cycle of the simulated environment, and the heating and cooling rates are consistent with the actual temperature curve of the simulated environment; the preset initial temperature is the highest temperature in the temperature curve range; the alternating low-temperature frozen soil environment is divided into freezing environment simulation and gradual melting environment simulation. When simulating a gradual melting environment, the highest temperature is higher than the freezing point of the corresponding real environment.

[0074] Specifically, the above-mentioned temperature range, heating and cooling rates, and heating and cooling times are determined according to the specific local meteorological and hydrological conditions, and are generally taken as monthly averages or extreme values, such as the monthly maximum temperature (obtained from the daily average), the average daily sunshine time of the month (obtained from the daily average), and the monthly minimum temperature (obtained from the daily average).

[0075] It is worth noting that the above simulation model is suitable for areas with large annual / monthly temperature fluctuations. The ambient temperature may be below freezing point all year round or above freezing point for a short time. This simulation model is mainly aimed at frozen soil in a frozen state. With the large changes in the temperature range, the chemical corrosion and physical corrosion (expansion or contraction) properties will also change, thereby causing a comprehensive and unpredictable corrosion to metal materials.

[0076] Specifically, a temperature curve of alternating low-temperature frozen soil environment used to simulate the environment of the northeastern Mohe basin in December is:

[0077] The temperature curve range is between -35°C and -20°C, and the preset initial temperature is -20°C;

[0078] Phase 1: Target temperature -35±1℃, cooling rate 0.5~10℃ / hour, keep warm after reaching the target temperature, for a total of 12~16h;

[0079] Phase II: Target temperature -20±1°C, heating rate 0.5-5°C / hour, keep warm after reaching the target temperature, for a total of 8-12 hours;

[0080] With a 24-hour cycle, the total detection time is 1 to 30 days.

[0081] Specifically, the maximum temperature T of the monthly temperature curve max >Local freezing point T0 and minimum temperature T min < local freezing point T0, and T max -T0≥T0-T min When the temperature drops to 0.05, it is determined that the simulated area is in a short-term frozen ground environment during the corresponding time period.

[0082] Specifically, when simulating a short-term frozen soil environment, the temperature curve range is between -5°C and 20°C, and the preset initial temperature is 20°C;

[0083] Phase 1: Target temperature -5±1°C, cooling rate 0.5-3°C / hour, keep warm after reaching the target temperature, for a total of 12-16 hours;

[0084] Phase II: Target temperature 20±1°C, heating rate 0.5-5°C / hour, keep warm after reaching the target temperature, for a total of 8-12 hours;

[0085] The first and second stages total 24 hours;

[0086] With a cycle of 24 hours, the total detection time is 1 to 30 days, for example, 1, 2, 3, 5, 10, 15, 20, 25, and 30 days.

[0087] Specifically, since the short-term frozen soil environment is relatively mild, unless there is a special need, the above-mentioned general temperature curve can be used for corrosion simulation, and the simulation evaluation results still have high reliability and reference value.

[0088] It is worth noting that, whether it is an alternating low-temperature frozen soil environment or a short-term frozen soil environment simulation, the cooling and warming rates are variable. The specific cooling and warming rates can be changed according to the actual temperature curve of the simulated environment, such as slow first and then fast, fast first and then slow, etc.

[0089] Specifically, different months in the area to be simulated may belong to different types of frozen soil environments. The actual simulation evaluation can be implemented by combining different types of temperature curve cycles. From an engineering perspective, soil containing solid water and frozen for two years or more should be determined as permafrost, also known as permafrost. Seasonal frozen soil refers to soil or loose rock layers that freeze in winter and melt in spring. The depth of the frozen soil layer is determined by factors such as natural geographical conditions and soil physical properties. This type of frozen soil will undergo periodic freezing and thawing with seasonal changes, that is, it freezes when the temperature drops below freezing in winter and melts when the temperature rises in spring. Short-term frozen soil refers to frozen soil with a freezing period of several hours to half a month. This type of frozen soil is characterized by a shorter freezing period and usually does not last for a long time. Compared with seasonal frozen soil and permafrost (permafrost), short-term frozen soil has a shorter freezing and thawing cycle and relatively less impact on engineering construction and the natural environment.

[0090] For example, if a certain area has seasonal frozen soil, then a constant temperature frozen soil environment simulation can be used from November to February (winter), and an alternating low temperature frozen soil environment simulation and / or a short-term frozen soil environment simulation can be used from March to October (spring, summer, and autumn). Different temperature curves are used to perform different numbers of cycles in sequence to simulate the corrosion conditions in different time periods, and finally the annual corrosion rate is calculated or estimated by weighting and other methods.

[0091] Preferably, the metal sample can adopt two shapes, and the specific specifications are as follows:

[0092] Plate specimen: Dimensions: length l × width b × thickness h;

[0093] Circular specimen: External dimensions: diameter φ × thickness h;

[0094] l, b, φ≤100mm, h is 2-5mm, and the surface area of ​​each sample is ≥10cm 2The shape and size of the specimen depend on the original condition of the test material and the test container used. Specimens with a large surface area per unit mass and a small ratio of side surface area to total surface area should be used whenever possible. Generally, the area perpendicular to the rolling or forging direction should not exceed half of the total specimen area, but the specimen should not be too large. Specimens of other shapes and sizes may be used depending on the test purpose. The specimen is suspended in the solution.

[0095] Specifically, the internal gas atmosphere includes nitrogen and oxygen, Vnitrogen: Voxygen=7~8:3~2, and the internal gas atmosphere pressure is 50~100kPa. Since metal materials are actually buried or semi-buried underground, the influence of atmospheric corrosion is relatively small, and its influence is omitted in the present invention; however, oxygen in the atmosphere has an important influence on metal corrosion in the soil. It not only participates in the metal oxidation reaction, but also acts as an electron acceptor in the corrosion process, accelerating the occurrence and development of corrosion. The corrosion rate of oxygen on metals increases with increasing temperature and concentration, and the presence of water will also accelerate the corrosion rate of metals. In order to restore the air pressure conditions of the permafrost environment as much as possible (generally speaking, permafrost environments are mostly plateaus with low air pressure) and atmospheric components, the present invention can adjust the composition and air pressure of the circulating gas so that the simulated corrosion process is as close to the actual situation as possible.

[0096] Specifically, the specific operations of step S4 are:

[0097] S4-1: Make the metal to be tested into metal samples of certain specifications, weigh the metal samples and record the weight;

[0098] S4-2: Completely immerse the metal sample in the simulated corrosion solution, place the container containing the simulated corrosion solution in a closed simulation chamber and pre-temperature it;

[0099] S4-3: According to a preset temperature curve, a temperature-controllable circulating gas is introduced into the closed simulation chamber to adjust the temperature in the simulation chamber and start timing, so that the temperature in the chamber changes according to the preset temperature curve;

[0100] S4-4: After the preset detection time is reached, the corroded metal sample is taken out and cleaned to remove the surface corrosion part, and the corrosion amount is calculated based on the weight difference before and after.

[0101] Specifically, the specific operation of pre-temperature adjustment in step S4-2 is: closing the simulation chamber and starting temperature adjustment, and proceeding to the next step when the simulated corrosion solution and the metal sample reach the preset initial temperature; the pre-temperature adjustment time is 0.5 to 2 hours, the purpose of which is to avoid a large difference between the target temperature and the initial temperature, which will cause the temperature of the simulated corrosion solution and the metal sample to fail to reach the preset temperature curve.

[0102] Specifically, the specific composition of the simulated corrosion solution is calculated by mass percentage as follows: Na2SO4 0.06-1%, MgCl2 0.05-0.1%, NaCl 3-5%, and the rest is deionized water; the pH value of the simulated corrosion solution is 6-8. The hydrological conditions in permafrost areas are very different from those in plain areas. Taking the salt lake area as an example, it has gradually desalinated due to the warming and humidification of the Qinghai-Tibet Plateau climate. The downstream Qingshui River has changed from brackish water to salt water due to the discharge of the salt lake; the perennial surface water such as the salt lake and the Qingshui River and their shallow groundwater are all of the Cl·SO4-Na type, with evaporation and crystallization as the main factors, while the chemical type of the northern river water is HCO3-Mg·Ca, and its shallow groundwater has a similar ion composition to the deep groundwater of the Qingshui River. The water quality is weakly alkaline as a whole, and the pH value fluctuates between 7.8 and 8.5 with different seasons. The cation in the water is mainly Ca 2+ Mg 2+ The main anion is Cl - 、SO4 2- 、HCO3 - Mainly, among which Cl - Ion concentration 40~190mg / l, SO4 2- Ion concentration 8~25mg / l, HCO3 - The ion concentration is 190~480mg / l, which varies with the seasons. The water chemical composition is mainly affected by rock weathering and dissolution. The main component and correlation analysis show that Na + , K + 、Cl - Mg 2+ and SO4 2- Mainly derived from evaporative salt rocks such as rock salt and magnesium sulfate, Ca 2+ 、HCO3 - It mainly comes from silicate rocks such as dolomite and anorthite. - 、SO4 2- 、HCO3 - Plasma will corrode metals, so when using steel for highway construction in this area, it is necessary to consider the corrosion resistance requirements of these ions; among them, Cl - 、SO4 2- Theoretical analysis and experimental verification show that the composition of the simulated corrosion solution can basically restore the metal corrosion situation in a frozen soil environment.

[0103] It is worth noting that due to the long duration of corrosion experiments, when accelerated experiments are required, the concentration of the reagents needs to be increased accordingly, and the ambient temperature needs to be appropriately raised to speed up the reaction. The temperature control curve adjustment period needs to be adjusted synchronously with the acceleration ratio. When temperature alternation and freeze-thaw cycles affect the corrosion rate, the purpose of accelerating corrosion can be achieved by shortening the heating / cooling time and increasing the number of cycles.

[0104] Furthermore, in order to simulate the impact of physical damage to the surface of metal materials caused by freeze-thaw on corrosion, a portion of sand and soil components can be added to the simulated solution. The sample is inserted into the sand and soil and is completely covered by the simulated corrosion solution to simulate the additional wear caused by the volume change of soil freezing in an alternating environment. The corrosion conditions of the metal sample buried in the sand and soil will be closer to the corrosion conditions in a real environment.

[0105] The present invention also provides a device for implementing the simulation evaluation method designed by the design method: the device comprises two parts: a temperature control module (1) and a simulation test module, the temperature control module is used to control the temperature change inside the simulation test module, and the simulation test module is used to implement a full immersion corrosion simulation corrosion test of a metal sample.

[0106] The temperature control module 1 includes a heat exchange medium circulation system composed of a radiator 13, a four-way reversing valve 11, a first heat exchanger 16, a second expansion valve 151, and a first expansion valve 141 connected in sequence. The four-way reversing valve 11 is also connected to the compressor 12. The first expansion valve 141 is provided with a first check valve 142 in parallel. The second expansion valve 151 is provided with a second check valve 152 in parallel.

[0107] The simulation test module includes a closed simulation chamber 2, inside which a second heat exchanger 21, a circulating fan 22, a sample pool 23 and a sensor 25 are provided. The second heat exchanger 21, the sample pool 23 and the circulating fan 22 are arranged in sequence to form an annular air path. It is worth noting that the components arranged in sequence here are not physically connected, but are merely arranged in sequence on the gas circulation path / annular closed path to achieve temperature control of the closed simulation chamber 2. The sensor 25 is arranged in the middle and upper part of the sample pool 23. The simulation chamber is provided with an exhaust hole, and a negative pressure filter 24 is provided at the exhaust hole.

[0108] The first heat exchanger 16 and the second heat exchanger 21 are installed close to each other to achieve contactless heat exchange.

[0109] The temperature control module 1 uses a reverse Carnot cycle to control the temperature of the simulation test module by changing the flow of heat. The first heat exchanger 16 is placed in the environment to exchange heat with the atmosphere; the first heat exchanger 16 uses an isolated design to exchange heat with the simulation test module (primarily the second heat exchanger 21).

[0110] When cooling is required, the heat pump flows heat from the second heat exchanger 21 to the first heat exchanger 16; after the temperature of the second heat exchanger 21 drops, it absorbs heat from the closed simulation chamber 2 circulation system, causing its temperature to drop; after the first heat exchanger 16 obtains heat, its temperature rises and it releases the heat to the surrounding atmosphere. When heating is required, the heat pump reverses, and heat flows from the first heat exchanger 16 to the second heat exchanger 21. At this time, the temperature of the first heat exchanger 16 drops and absorbs heat from the surrounding atmosphere; after the second heat exchanger 21 obtains heat, its temperature rises and it releases heat to the simulation chamber circulation system, raising its temperature. The second heat exchanger 21 itself is provided with an electric heater. When the surrounding environment lacks heat, the heater can be used for auxiliary heating to quickly increase the temperature of the simulation chamber;

[0111] The simulation test module uses an air-cooling design, simulating the sample's surrounding environment by varying the temperature and speed of the circulating air. Because the simulated corrosive solution is volatile, the circulating gas contains certain corrosive components. The enclosed simulation chamber 2 is corrosion-resistant to ensure its service life. The chamber is equipped with temperature, humidity, and pressure sensors 25 to monitor the current environmental conditions. The circulating system's gases are primarily nitrogen and oxygen, with their ratios and pressures set according to the atmospheric conditions of the simulated environment.

[0112] In order to protect the internal equipment and the surrounding environment, the temperature control module 1 and the simulation test module are isolated and exchange heat through the heat exchange system to prevent the simulated gas from affecting the temperature control module 1.

[0113] Specifically, the sample pool 23 is equipped with a matching reagent tank for holding the simulated corrosion solution. The reagent tank is provided with fins. To improve the heat exchange effect, fins are provided on the outside of the reagent tank along the airflow direction to increase the heat exchange area with the gas, allowing the reagent in the reagent tank to reach the predetermined temperature more quickly.

[0114] Specifically, the operating process / principle of the temperature control module 1 is as follows:

[0115] The various components within temperature control module 1 are connected by pipes containing a heat exchange medium. When cooling is required, the heat exchange medium enters through the inlet of compressor 12, undergoes compression, and transforms from a gas into a liquid. Heat is released through radiator 13. The liquid heat exchange medium passes through first check valve 142 and second expansion valve 151, causing it to evaporate due to the reduced pressure and transform into a gas. The heat is then absorbed by the heat exchanger.

[0116] The first heat exchanger 16 of the temperature control module 1 is installed close to the second heat exchanger 21. As the heat is transferred to the first heat exchanger 16, the temperature of the gas passing through the second heat exchanger 21 decreases, achieving the purpose of refrigeration. The refrigerated gas is pressurized by the circulating fan and enters the space where the sample pool 23 is located, and its temperature is reduced to simulate the low temperature environment of frozen soil (see Figure 1 ).

[0117] When it is necessary to simulate the thawing process of frozen soil, the four-way valve is reversed. The heat exchange medium is compressed from gas to liquid after passing through the compressor 12 and then enters the first heat exchanger 16, releasing heat at the same time. The liquid heat exchange medium passes through the second one-way valve 152 and the first expansion valve 141 and then turns into gas due to the pressure drop. It then exchanges heat with the outside air through the radiator 13 and returns to the compressor 12 through the four-way valve to complete the cycle. Figure 2 ).

[0118] Cooling and heating are completely completed by the heat pump system. A sensor 25 is set in the closed simulation chamber 2 to control the cooling and heating amount according to the current temperature so that the environment in the chamber meets the detection needs.

[0119] The temperature control module 1 and the simulation test module (enclosed simulation chamber 2) are isolated from each other, and the gases between the two are not connected, so as to prevent the corrosive gases generated by the volatilization of the reagents in the sample pool 23 from affecting the equipment; the simulation chamber adopts a closed design and is also equipped with a negative pressure filter 24, which can extract and purify the gas in the chamber before discharging it when the sample is placed in and taken out, so as to avoid the direct discharge of corrosive gases and cause environmental pollution.

[0120] Application Examples

[0121] Taking the metal corrosion simulation of the frozen soil environment (December) in the Mohe Basin in Northeast China as an example, the following Figure 1 The device shown is used to perform corrosion simulation evaluation on four types of steel to be tested, namely Q235 steel, Q460 steel, Q690 steel, and Ni-Cr-Mo-V low alloy high strength steel.

[0122] According to the average temperature curve of Mohe in December ( Figure 4 ) It can be seen that the highest temperature is around -20℃ and the lowest temperature is around -35℃, which belongs to the alternating freezing environment in the alternating low-temperature permafrost environment. The average daily sunshine time in Mohe in December is about 7.5 to 8 hours.

[0123] The temperature curve is:

[0124] The temperature curve range is between -35℃ and -20℃, and the preset initial temperature is -20℃;

[0125] Phase 1: Target temperature -35±1℃, cooling rate 0.5~10℃ / hour, keep warm after reaching the target temperature, for a total of 16 hours;

[0126] Phase II: Target temperature -20±1℃, heating rate 0.5~5℃ / hour, keep warm after reaching the target temperature, for a total of 8 hours;

[0127] With a cycle of 24 hours, the total detection time is 3 days.

[0128] According to the China Soil Database, soils in the Mohe region have a soluble salt content of 0.6-1.0%. The anion composition is primarily chloride, with only a small amount of sulfate. The chloride-to-sulfate equivalent ratio is greater than 4, and the soil texture is mostly loamy clay. The soil is mostly slightly alkaline, with a pH of 7.4-8.4, and the exchangeable bases are primarily calcium and magnesium ions.

[0129] Prepare a simulated corrosion solution consisting of 0.06% Na2SO4, 0.1% MgCl2, 3.5% NaCl, and the remainder deionized water, pH = 8;

[0130] Sample specifications: 50mm×40mm×3mm;

[0131] Sand addition amount: 80g / L (based on the total volume of simulated corrosion solution);

[0132] Circulating gas parameters: Nitrogen:Oxygen (volume ratio) = 8:2, gas pressure 95kPa; (the local air pressure in Mohe is about 95kPa)

[0133] The corroded metal sample is removed and cleaned to remove the surface corrosion. The corrosion rate is calculated by the weight difference before and after. The corrosion rate calculation formula is as follows:

[0134]

[0135] X---------Test piece corrosion rate, mm / a

[0136] W1--------Weigh the test piece before testing, g

[0137] W2--------Weight of test piece after test, g

[0138] 87600----Calculation constant

[0139] A---------surface area of ​​test piece, cm 2

[0140] T----------Test time, h

[0141] D---------test piece material density, g / cm 3

[0142] Table 1 Summary of the simulated corrosion results of each sample in alternating low temperature environment

[0143]

[0144] Since the corrosion rate decreases with decreasing temperature, in the simulation of the Mohe environment in December, although the corrosion resistance of several samples varies, the absolute difference in corrosion rate is relatively small. Samples 1 to 3 have similar material prices and corrosion rates, and their strengths differ by 2 to 3 times. Therefore, high-strength materials can be selected. After calculating the total cumulative corrosion thickness based on a 20-year service life, it is sufficient to leave a sufficient thickness margin during structural design. Sample 4 (Ni-Cr-Mo-V low-alloy high-strength steel) has the best corrosion resistance, but its cost is 3 to 4 times that of the other samples. Unless extreme environments or applications have restrictions on the weight of the material structure, samples 2 and 3 (Q460 steel and Q690 steel) are sufficient to meet construction needs. Compared with samples buried in the field, the corrosion rate error is ≤5%, which can meet the needs of corrosion resistance evaluation and preliminary screening of metal materials.

[0145] This test screens materials solely for corrosion resistance; specific material selection should be considered in conjunction with their low-temperature mechanical properties. The examples below assess corrosion resistance over a specific time period in a specific region. Calculating cumulative corrosion requires taking a weighted average of each time period throughout the year and then calculating the annual average corrosion rate.

[0146] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A design method for evaluating the corrosion resistance of metals in frozen soil environments, characterized in that: The specific steps include: S1: Collect monthly temperature curves, air pressure variation range, atmospheric composition, hydrology and soil composition information of the area to be simulated; S2: Design and prepare a test device based on the upper and lower limits of the temperature curve, determine the composition of the simulated corrosion solution based on the hydrological and soil composition information, and prepare the simulated corrosion solution; S3: Preset the temperature curve according to the annual and monthly temperature curves, and adjust the gas atmosphere inside the testing device according to the air pressure variation range and the atmospheric composition information; S4: The metal to be tested is made into a metal sample of a certain specification, and a full immersion corrosion simulation experiment is performed using the test device and the simulated corrosion solution for at least one temperature curve cycle, and the corrosion behavior and corrosion resistance of the corresponding metal in a frozen soil environment are estimated based on the corrosion simulation results; wherein one temperature curve cycle is 24 hours; The specific operations of step S4 are: S4-1: Make the metal to be tested into metal samples of certain specifications, weigh the metal samples and record the weight; S4-2: Completely immerse the metal sample in the simulated corrosion solution, place the container containing the simulated corrosion solution in a closed simulation chamber and pre-temperature it; S4-3: According to a preset temperature curve, a temperature-controllable circulating gas is introduced into the closed simulation chamber to adjust the temperature in the simulation chamber and start timing, so that the temperature in the chamber changes according to the preset temperature curve; S4-4: After the preset detection time is reached, the corroded metal sample is removed and cleaned to remove the surface corrosion. The corrosion amount is calculated based on the weight difference before and after. The permafrost environment is a high-altitude permafrost environment; The specific composition of the simulated corrosion solution is calculated by mass percentage as follows: Na2SO4 0.06-1%, MgCl2 0.05-0.1%, NaCl 3-5%, and the rest is deionized water; the pH value of the simulated corrosion solution is 6-8.

2. The design method according to claim 1, characterized in that: The maximum temperature T of the monthly temperature curve max Not higher than the local freezing point T0 and the difference between the upper and lower limits of the monthly temperature curve T max -T min ≤10℃, it is determined that the simulated area is a constant temperature frozen soil environment in the corresponding time period.

3. The design method according to claim 1, characterized in that: The difference between the upper and lower limits of the monthly temperature curve T max -T min >10℃ and the maximum temperature T max ≤ local freezing point T0, it is determined that the simulated area is in an alternating freezing environment during the corresponding time period; The difference between the upper and lower limits of the monthly temperature curve T max -T min >10℃ and the maximum temperature T max >Local freezing point T0, and T max -T0<T0-T min When , it is determined that the area to be simulated is an alternating and gradual melting environment in the corresponding time period; The alternating freezing environment and the alternating gradual thawing environment are collectively referred to as alternating low-temperature permafrost environment.

4. The design method according to claim 1, characterized in that: The maximum temperature T of the monthly temperature curve max >Local freezing point T0 and minimum temperature T min < local freezing point T0, and T max -T0≥T0-T min When the temperature drops to 0.05, it is determined that the simulated area is in a short-term frozen ground environment during the corresponding time period.

5. The design method according to any one of claims 2 to 4, characterized in that: Different months in the simulated area may belong to different permafrost environment types. The actual simulation evaluation can be implemented by combining different types of temperature curve cycles.

6. The design method according to claim 3, characterized in that: The alternating low-temperature frozen soil environment temperature curve used to simulate the environment in the northeastern Mohe Basin in December is: The temperature curve range is between -35°C and -20°C, and the preset initial temperature is -20°C; Phase 1: Target temperature -35±1℃, cooling rate 0.5~10℃ / hour, keep warm after reaching the target temperature, for a total of 12~16h; Phase II: Target temperature -20±1°C, heating rate 0.5-5°C / hour, keep warm after reaching the target temperature, for a total of 8-12 hours; With a 24-hour cycle, the total detection time is 1 to 30 days.

7. The design method according to claim 1, characterized in that: The internal gas atmosphere includes nitrogen and oxygen, Vnitrogen:Voxygen=7-8:3-2, and the internal gas atmosphere pressure is 50-100 kPa.

8. A device for implementing the simulation evaluation method designed by the design method according to any one of claims 1 to 7, characterized in that: The device comprises two parts: a temperature control module (1) and a simulation test module. The temperature control module is used to control the temperature change inside the simulation test module. The simulation test module is used to implement a full immersion corrosion simulation corrosion test on a metal sample.

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